Figure 1

The low-energy electron diffraction pattern of ${\mathrm{BaNi}}_2$${\mathrm{As}}_2$ in the triclinic phase taken with 100-eV incident electrons.Reuse & Permissions

Figure 2

Photoemission data of ${\mathrm{BaNi}}_2$${\mathrm{As}}_2$. (a) Photoemission intensity map at the Fermi energy ($E_F$) measured at 150 K in the tetragonal phase. For the convenience of data presentation, the two-dimensional (2D) Brillouin zone is referred to hereafter, which is the projection of three-dimensional (3D) Brillouin zone. (b) Photoemission intensity plots of cuts 1–16 as indicated in panel (a). (c) and (d) are the same as panels (a) and (b) but for data measured at 13 K in the triclinic phase. Band dispersions are indicated by the dashed curves. Data were taken in HSRC with circularly polarized 22.5-eV photons. Labels are explained in the text.Reuse & Permissions

Figure 3

Photoemission data along several cuts parallel to $\mathrm{\Gamma ̄}$-$\mathrm{X̄}$ in the triclinic phase. (a)–(e) Photoemission intensity plots of cuts 1–5 as indicated in panel (g), taken in the HSRC with circularly polarized 21.2-eV photons at 20 K. (f) Photoemission intensity plot of cut 6 as indicated in panel (g), taken with randomly polarized 21.2-eV photons from a helium lamp at 25 K. (g) The momentum distribution curves (MDCs) corresponding to panel (f). (h) Cuts 1–6 are indicated in the projected 2D Brillouin zone. The dashed curves and markers trace the band dispersions.Reuse & Permissions

Figure 4

Photoemission data along $\mathrm{\Gamma ̄}$-$\mathrm{M̄}$ measured at 10 K in the triclinic phase with 100-eV linearly polarized light at the SLS. (a) Experimental setup for the $s$- and $p$-polarization geometries and the indication of the $\mathrm{\Gamma ̄}$-$\mathrm{M̄}$ cut in the projected 2D Brillouin zone. (b) and (c) Photoemission intensity plots measured in the $s$- and $p$-polarization geometries, respectively. The image contrast in the rectangular region as enclosed by dashed-dotted lines in panel (c) is adjusted to reveal the bands in this region. (d) Stack of MDCs in the $s$- and $p$-polarization geometries. Each MDC is normalized by its integrated weight. Dashed curves and markers trace the band dispersions. Labels are explained in the text.Reuse & Permissions

Figure 5

Temperature dependence of photoemission data. (a) Indication of the cut by the thick line in the projected 2D Brillouin zone. (b) and (c) Photoemission intensity plots along the cut shown in panel a measured at 145 and 12 K, respectively. (d) Comparison of energy-distribution curves (EDCs) at $k_{\parallel }=0$ for data shown in panels (b) and (c). Data were taken in HSRC with circularly polarized 22.5-eV photons for panels (b)–(d). (e) EDCs at $k_{\parallel }=0$ for a cooling-warming-cooling cycle, measured with randomly polarized 8.4-eV photons from a xenon discharge lamp. The short bars indicate the peak positions. (f) Summary of peak positions obtained from panel (e), which exhibits a hysteresis.Reuse & Permissions

Figure 6

(a) Band structure along $\mathrm{X̄}$-$\mathrm{\Gamma ̄}$-$\mathrm{M̄}$ in the triclinic phase summarized from Figs. 3 and 4. (b) Calculated band structures in the tetragonal (dashed curves) and triclinic (solid curves) phases.[34] (c) Experimental band structure from panel (a) (dashed curves) overlaid by the calculated band structure (solid curves) in the triclinic phase. The energy scale of the calculated band structure at the right side is 1.66 times the energy scale of the experimental one on the left side. The summary of experimental Fermi contours (d) in the tetragonal phase and (e) in the triclinic phase, respectively. The small circles indicate the small Fermi surfaces around $\mathrm{\Gamma ̄}$, and the dashed circles indicate the Fermi surface around $\mathrm{X̄}$. The sketches are depicted, in part, for the projected 2D Brillouin zone. (f) and (g) The calculated 3D Fermi surfaces in the tetragonal and triclinic phases, respectively.[34] (h) The 3D tetragonal Brillouin zone (thick lines) with notations for high-symmetry points. Labels are explained in the text.Reuse & Permissions

Figure 7

(a) Illustration of the in-plane spatial symmetry of $3d$ orbitals. (b)–(f) Contributions of the $d_{\mathit{xy}}$, $d_{\mathit{yz}}$, $d_{x^2-y^2}$, $d_{z^2}$, and $d_{\mathit{xz}}$ orbitals to the calculated band structure of ${\mathrm{BaNi}}_2$${\mathrm{As}}_2$, respectively. The contribution is represented by both the size of the symbols and the color scale.Reuse & Permissions